Electrical Signal Application Strategies for Monitoring a Condition of an Elevator Load Bearing Member

ABSTRACT

An elevator load bearing member ( 30 ) monitoring device includes a controller ( 42 ) that applies a selected electrical signal to tension members ( 32 ) of the load bearing member ( 30 ). In one example, connectors ( 40 ) are associated with ends of the load bearing member ( 30 ) to establish an electrical interface between the controller ( 42 ) and the tension members ( 32 ). The connectors ( 40 ) facilitate establishing electrical circuit loops along the tension members ( 32 ) such that only non-adjacent tension members are energized at a selected time. A variety of circuit configurations are disclosed. The applied electrical signal in one example has a potential that is negative compared to a ground potential of a hoistway in which the elevator belt is used. In another example, the electrical signal comprises a plurality of pulses and has a duty cycle that is on the order of about one percent.

FIELD OF THE INVENTION

This invention generally relates to monitoring load bearing members inelevator systems. More particularly, this invention relates to a circuitarrangement for using electricity-based monitoring techniques.

DESCRIPTION OF THE RELATED ART

Elevator systems often include a car and counterweight that aresuspended by a rope or belt arrangement. A drive machine moves the ropeor belt to cause the desired movement of the car to different levelswithin a building, for example. Traditionally, steel ropes were used.More recently, other types of load bearing assemblies have beenintroduced. One example is a coated steel belt having a plurality ofsteel cords encased in a polyurethane jacket.

With the introduction of new belts, the need for new monitoringtechniques has arisen to check the quality of the belt over time. Thejackets over the tension members prevent visual inspection. Coated steelbelts are believed to have extended service lives, however, it isadvisable to monitor the condition of them to detect any degradation inthe strength of the tension members within the belt (i.e., the steelcords). A variety of monitoring techniques are being developed.

One approach is to use electricity for determining the characteristicsof the tension members and, therefore, the strength of the belt. Oneexample technique relies upon the fact that the cross-sectional area ofa steel cord tension member is directly related to the electricalresistance of that member. Accordingly, monitoring the resistance of thetension members provides an indication of the condition of the tensionmembers.

In order to utilize a resistance based inspection technique, anefficient strategy is required for arranging electrical circuits so thatthe resistance of the tension members can be determined. This inventionaddresses that need by providing unique circuit arrangements andstrategic electrical signal characteristics to enable effectivemonitoring of the tension members in a coated steel belt, for example.

SUMMARY OF THE INVENTION

In general terms, this invention is a circuit arrangement that enablesefficient electricity-based monitoring of an elevator load bearingmember.

One example method includes applying an electric signal that comprises aplurality of pulses and has a duty ratio that is less than about tenpercent to at least one of the tension members. In one example, the dutycycle is less than about one percent. A low duty ratio minimizes theamount of electrical energy carried by the tension members, which tendsto reduce the possibility for any corrosion resulting from using thetension members as conductors of electricity.

Where a load bearing member has a plurality of spaced, electricallyconductive tension members, an example method includes strategicallyapplying electric signals only to tension members that are not adjacentto each other to avoid establishing an electric field between the spacedapart tension members. This technique avoids any corrosion ordegradation of the tension members that may otherwise be caused by theintroduction of electricity along the tension members.

In one example, at least two non-adjacent tension members areelectrically coupled so that the electric signal is applied to thecoupled tension members, which form a loop or circuit along which theelectric signal is propagated.

According to one example, the electric signal applied to the tensionmembers is chosen so that the tension members are effectively cathodesrelative to a hoistway where the load bearing member is used. This isaccomplished in one example by controlling a potential of the electricalsignal such that the potential is negative compared to a groundpotential of the hoistway.

In another example, the electric signal is applied only to non-adjacenttension members at a given time.

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates selected portions of an elevator systemincluding an elevator load bearing member monitoring assembly designedaccording to an embodiment of this invention.

FIG. 2 is a perspective illustration of a portion of an elevator beltschematically illustrating an electrical connector useful with anembodiment of this invention.

FIG. 3 schematically illustrates an example circuit configurationdesigned according to an embodiment of this invention.

FIG. 4 schematically illustrates another circuit configuration.

FIG. 5 illustrates another circuit configuration.

FIG. 6 illustrates another example circuit configuration.

FIG. 7 illustrates another example circuit configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows an elevator system 20 where a car 22 andcounterweight 24 move within a hoistway 26. A drive machine 28 causesmovement of a load bearing member 30, which results in the desiredmovement of the car 22 and corresponding movement of the counterweight24. The movement of the elevator system is known.

As shown in FIG. 2, an example load bearing member 30 is a coated steelbelt having a plurality of steel cord tension members 32 encased in apolyurethane jacket 34. As can be appreciated form the drawing, thetension members 32 comprise a plurality of steel strands wound into acord in a known manner. The jacket material 34 generally surrounds eachof the tension members and fills spaces between them. The tensionmembers 32 extend longitudinally (as shown by L in FIG. 2) in parallelalong the length of the belt 30. This invention is not limited to aspecific kind of load bearing member.

FIG. 2 also shows a connector 40 for establishing an electricalconnection with the tension members 32. Although not specificallyillustrated, in one example the connector 40 includes connector membersthat pierce through the jacket material 34 to establish an electricalconnection with at least selected ones of the tension members 32. Theconnectors 40 in the example of FIG. 1 are attached to each end of thebelt 30 and provide an electrical interface for coupling the tensionmembers 32 with a controller 42 that is suitably programmed to conduct aselected electricity-based monitoring technique. The example connector40 includes a first portion 46 and a second portion 48 received onopposite sides of the belt 30. Securing members 50 allow the connectors40 to be secured in a desired position near the ends of the example belt30.

The controller 42 preferably monitors the condition of the tensionmembers 32 and, therefore, the condition of the belt 30 by monitoring aselected electrical characteristic of the tension members. In oneexample, the resistance of each tension member is monitored to makedeterminations regarding the cross-sectional area of the tensionmembers, which provides an indication of localized strain or degradationof the tension members over time. This description includes a variety ofcircuit arrangements for enabling the controller 42 to make thenecessary determinations. The example controller 42 includes anohm-meter portion 44 that makes a determination regarding the electricalresistance of the tension members 32, respectively.

FIG. 3 schematically illustrates one example circuit geometry designedaccording to an embodiment of this invention. In this example, eachtension member 32A-32L is individually coupled with the controller 42.Each tension member accordingly establishes its own circuit asschematically shown in FIG. 3 (although the connections between thecontroller 42 and the tension member 32A are the only connectionsspecifically illustrated). A similar connection is made with each of theindividual tension members. One advantage to such an arrangement is thatit allows for individually monitoring any one of the tension members.Alternatively, such an arrangement allows for monitoring every tensionmember simultaneously. If all tension members are powered appropriately,there is no inter-cord corrosion risk as there would be no potentialdifference between the tension members.

One possible source of corrosion risk may occur when a sufficientelectric field is established between the cords such that ions maymigrate between tension members. Minimizing such migrating ionsminimizes corrosion risk.

Another example arrangement is shown in FIG. 4 where the tension members32A and 32G establish a single circuit loop that is monitored as thecontroller 42 applies an electrical signal to that circuit. In thisexample, one of the connectors 40 establishes the interface with thecontroller 42. The other connector 40 includes an electric coupling 60that couples the tension members 32A and 32G together to establish thecircuit loop. In this example, the tension members are grouped in sixsets of two so that the first and seventh (i.e., 32A, 32G) tensionmembers form one circuit while the second and eighth form anothercircuit. Similarly, the sixth and twelfth tension members form acircuit. Using such a strategy maintains maximum distance between twotension members that are energized simultaneously for carrying anelectric signal applied by the controller 42. Maintaining a maximumdistance between the conducting tension members minimizes the corrosionrisks associated with migrating ions that may migrate across the belt 30because of the electric field established between tension members. Byutilizing non-adjacent tension members to establish a circuit loop, theinventive approach minimizes the risk of corrosion otherwise associatedwith the application of electricity to the tension members.

It should be noted that FIG. 4 shows only one electrical coupling 60although six of them are used to establish the six separately circuitloops along the belt 30. One advantage to an arrangement as shown inFIG. 4 is that only one of the connectors 40 is required for making anactual connection with the controller 42, which minimizes the complexityor expense of the electrical coupling (i.e., wiring) between theconnectors 40 and the controller 42. The electrical couplings 60 withinthe connector 40 at one end of the belt 30 can effectively be internalto the connector so that no outside wiring is required near that end ofthe belt.

FIG. 5 illustrates another example circuit arrangement. In this example,four groups of three tension members are electrically coupled usingelectrical couplings 60 and 62 to establish circuit loops. In someinstances, the length of the belt 30 may be too short for an individualtension member (or even two tension members) to establish a circuit longenough to achieve a signal-to-noise ratio that enables accurate enoughmonitoring. An arrangement as shown in FIG. 5 facilitates establishing abetter signal-to-noise ratio for relatively shorter belts by increasingthe number of tension members within a single circuit loop. In thisexample, the tension members 32A, 32E and 321 establish a first circuitloop. The tension members 32B, 32F and 32J establish another loop.Similarly, two additional loops are established with the preference tomaintain a maximum feasible distance between tension members that willbe energized at any given time. By energizing only non-adjacent tensionmembers, the inventive approach minimizes the risk of corrosion of thetension members.

FIG. 6 illustrates another example that has the advantage like FIG. 4where the connections with the controller 42 are established by a singleone of the connectors 40. In this example, four tension members 32A,32D, 32G and 32J establish a single circuit loop. Three electricalcouplings, 60, 62 and 64, are required to establish the loop. One of theconnectors 40 includes the couplings 60 and 64 and does not require anyexternal wiring, which may be advantageous in many circumstances.Although not specifically illustrated, an arrangement as shown in FIG. 6used with a belt having twelve tension members preferably includes threesets of four tension members coupled into a single circuit loop.

FIG. 7 illustrates still another example where two circuit loops areestablished by electrically coupling six of the tension members togetherinto a single circuit loop. In FIG. 7, the tension members 32A, 32C,32E, 32G, 32I and 32K are coupled together into a single circuit loop.Electrical couplings 60, 62, 64, 66 and 68 establish the circuit loop.The other tension members are grouped into a second circuit. Such anarrangement minimizes the number of circuits that need to be monitoredusing the controller 42. The distance between tension members energizedat the same time is reduced compared to the example of FIG. 4, forexample, however this may be advantageous, depending on the needs of agiven situation. Those skilled in the art who have the benefit of thisdescription will be able to select an appropriate arrangement to bestmeet the needs of their particular situation.

In each of the described examples, the belt 30 has twelve tensionmembers extending along the length of the belt. Of course, other circuitarrangements for different numbers of tension members may be morebeneficial. Those skilled in the art who have the benefit of thisdescription will realize what circuit arrangement works best for theirparticular situation.

Another feature of some examples is to strategically control theelectrical signal applied to the tension members 32 to further reducethe risk of corrosion. Increasing the lateral distance between thetension members that have an electrical potential difference betweenthem is one technique for reducing the possibility for establishing aconducting electrolytic pathway between energized cords. Another featureof some examples is to limit the maximum operating potential applied tothe tension members 32. In one example, the maximum voltage is 2 volts.An effective monitoring signal may have a potential between 0 and 2volts, for example.

In another example, the electrical signal comprises a plurality ofpulses and has a very low duty cycle so that the “on” time of the signalis very low. In one example, the duty cycle is less than or equal toabout one percent, which minimizes the time during which the electricalpotential is applied to the tension members 32. Minimizing the on timeof the electrical signal further minimizes the possible corrosion risk.

In another example, the electrical signal is selected to have a polaritythat establishes the tension members 32 as cathodes relative to theenvironment in which the belt 32 is used. For example, the electricalpolarity of the signal is negative compared to the effective ground ofthe hoistway 26. Applying an electrical signal of this characteristicreduces a corrosion risk in the event that a stray current pathway wereestablished between the tension members and the hoistway or buildingground.

A variety of techniques for minimizing the corrosion risk that otherwisemay be present when applying electricity to the tension members in anelevator load bearing member have been described. A combination of twoor more of the above-described techniques further reduces the corrosionrisk and enables efficient electricity-based monitoring of an elevatorbelt.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this invention. The scope of legal protection given tothis invention can only be determined by studying the following claims.

1. A method of monitoring a condition of an elevator load bearing memberthat has a plurality of spaced, electrically conductive tension members,comprising the steps of: applying a selected electric signal comprisinga plurality of pulses and having a duty ratio that is less than about10% to at least one of the tension members.
 2. The method of claim 1,including applying the signal to one of the tension members at a time.3. The method of claim 1, including coupling at least two non-adjacenttension members in an electrically conductive manner and applying theelectric signal to the coupled tension members.
 4. The method of claim1, including establishing the tension member carrying the signal as acathode relative to a hoistway where the belt assembly is used.
 5. Themethod of claim 4, including controlling a potential of the electricsignal such that the potential is negative compared to a groundpotential of the hoistway.
 6. The method of claim 1, wherein theelectric signal is applied only to non-adjacent tension members at atime.
 7. The method of claim 1, including determining a resistance ofthe tension members based upon the applied signal.
 8. A device formonitoring a condition of an elevator load bearing member comprising: acontroller that selectively applies an electric signal that comprises aplurality of pulses and has a duty ratio that is less than about 10% toat least one tension member.
 9. The device of claim 8, including aconnector that establishes an electrically conductive connection betweenthe controller and the tension member.
 10. The device of claim 9,wherein the connector includes at least one coupling that couples atleast two non-adjacent tension members together.
 11. The device of claim8, wherein the controller applies the electric signal such that thetension member carrying the signal is a cathode relative to a hoistwaywhere the belt assembly is used.
 12. The device of claim 11, wherein theelectric signal has a polarity that is negative compared to a groundpotential of the hoistway.
 13. The device of claim 8, wherein theelectric signal is applied only to non-adjacent tension members at atime.
 14. The device of claim 8, wherein the controller determines aresistance of the tension members and determines a condition of the loadbearing member based upon the determined resistance.
 15. The device ofclaim 8, wherein the controller applies the signal to an entireplurality of tension members simultaneously.
 16. An elevator loadbearing member assembly, comprising: a plurality of electricallyconductive tension members; a nonconductive jacket generally surroundingthe tension members; and a controller that selectively applies anelectric signal comprising a plurality of pulses and a duty ratio thatis less than about 10% to at least one of the tension members.
 17. Theassembly of claim 16, including a connector that establishes anelectrically conductive connection between the controller and thetension members.
 18. The assembly of claim 17, wherein the connectorincludes at least one coupling that couples at least two non-adjacenttension members together.
 19. The assembly of claim 16, wherein theelectric signal has a polarity that is negative compared to a groundpotential of a hoistway where the assembly is used.
 20. The assembly ofclaim 16, wherein the duty cycle is less than about 1%.